Chassis assembly

ABSTRACT

A chassis assembly is provided for use in subminiature wheeled toy vehicles or the like wherein the toy vehicle is adapted to coast due to gravity or to its own momentum upon the application of a pushing force. The chassis includes a relatively flat slug adapted to be secured to the underside of a vehicle body and has on its bottom surface a pair of downwardly opening recesses extending transversely to the direction of travel of the vehicle. A relatively flat elongated insert member formed of a plastic material is positioned on the bottom surface of the slug. The insert includes a pair of downwardly opening channels at opposite ends thereof, which channels are generally complementary to and received in respective ones of the slug recesses. The channels have opened end portions at opposite sides of the chassis and a wheel axis is loosely received in each of the channels with the ends of the axles extending through the openings and having a pair of wheels respectively secured thereto. A metal underplate is positioned on the bottom surface of the insert, substantially co-extensive therewith, with portions of the underplate covering the downwardly opened side of the channels to loosely retain the axles therein for rotation. Means are provided, integral with the slug, for securing the slug, insert and underplate together to form a unitary toy chassis assembly. The construction described is particularly suited for high speed assembly of sub-miniature toy vehicles.

United States Patent [191 Nielsen et al.

[451 Jan. 23, 1973 1 CHASSIS ASSEMBLY [75] Inventors: Edwin Nielsen, Oceanside, N.Y.;

Vincent Carella, Queens Village,

NY, [73] Assignee: Ideal Toy Corporation, Hollis, NY.

[22] Filed: Oct. 27, 1971 [21] Appl.No.: 193,065

UNITED STATES PATENTS 3,280,500 10/1966 Fairbairn ..46/20l 3,462,878 8/1969 Perryman et al. .....46/2()l 3,483,351 12/1969 Rix et al. t 4 ..46/20l 3 ,62 l ,609 LaBranche ..46/20l Primary ExaminerLouis G. Mancene Assistant ExaminerRobert F. Cuffing Att0rney-Richard M. Rabkin [5 7] ABSTRACT A chassis assembly is provided for use in subminiature wheeled toy vehicles or the like wherein the toy vehicle is adapted to coast due to gravity or to its own momentum upon the application of a pushing force. The chassis includes a relatively flat slug adapted to be secured to the underside of a vehicle body and has on its bottom surface a pair of downwardly opening recesses extending transversely to the direction of travel of the vehicle. A relatively flat elongated insert member formed of a plastic material is positioned on the bottom surface of the slug. The insert includes a pair of downwardly opening channels at opposite ends thereof, which channels are generally complementary to and received in respective ones of the slug recesses. The channelshave opened end portions at opposite sides of the chassis and a wheel axis is loosely received in each of the channels with the ends of the axles extending through the openings and having a pair of wheels respectively secured thereto. A metal underplate is positioned on the bottom surface of the insert, substantially co-extensive therewith, with portions of the underplate covering the downwardly opened side of the channels to loosely retain the axles therein for rotation. Means are provided, integral with the slug, for securing the slug, insert and underplate together to form a unitary toy chassis assembly. The construction described is particularly suited for high speed assembly of sub-miniature toy vehicles.

19 Claims, 6 Drawing Figures PATENTEDJAH 23 I975 SHEEI 1 [IF 2 IN VENTORS EDWIN NIELSEN BY VINCENT CARELLA VAHJ-HFDJM231975 3,71 1. 989

' SHEET 2 BF 2 INVENTORS EDWIN NIELSEN BY VINCENT CA RELLA W W KM; M7

CHASSIS ASSEMBLY The present invention relates to small wheeled toy vehicles and in particular to sub-miniature racing cars of the undriven type which are adapted to coast, due to gravity or to their own momentum, upon the application of a pushing force.

In some previously proposed toy vehicles of the above type, the wheel axles of the vehicle are mounted in or between a pair of protrusions which are bent about the axles so that they cannot drop out of their mounting. This conventional arrangement results in the wheels being subjected to a substantial amount of friction and thus limits the speed and the coasting range and travel distance of the vehicle. Other types of toy vehicles utilize separate bearing members for each axle mounting or at each point of connection of the axle to the vehicle body. This construction, while avoiding frictional problems, is relatively expensive because of the utilization of extra components and because of the additional manual labor required to assemble the various required bearing components. Since miniature toy vehicles must be produced relatively inexpensively, these procedures are not suitable for such toys.

In still other toy vehicles, the body portion of the vehicle itself forms part of the bearing mounting with the axles passed through aligned openings in the frames, or with the frame formed in two portions joined together with the axles therebetween. Such constructions are also relatively expensive and often, because of mismatch and malfitting of the parts, results in increased friction that limits travel distance for the vehicle.

In yet another form of toy vehicle construction, the axles are fixed to the chassis and each wheel is provided with its own bearing at its connection to one axle. Such construction obviously is complicated and requires multiple parts.

Accordingly, it is an object of the present invention to increase the speed or travel distance of undriven miniature toy vehicles which move under the influence of gravity or of their own momentum upon the application of a pushing force thereto.

Another object of the present invention is to simplify and improve the assembly and mounting of wheel axles on a vehicle body.

Yet another object of the invention is to provide an interchangeable chassis member having a unitary axle bearing assembly.

Still another object of the present invention is to provide sub-miniature toy vehicles of the above type which are relatively inexpensive to produce, simple to manufacture, and which have a relatively long useful life.

In accordance with an aspect of the present invention a presently preferred embodiment of a chassis assembly is provided for use in a sub-miniature wheeled toy vehicle or the like wherein the toy vehicle is adapted to coast over a substantial travel distance due to its own momentum upon the application ofa pushing force thereto. By sub-miniature is ment a chassis having an overall length of less than 1 inch. The chassis includes, as a main component, a relatively flat slug, formed of a die cast, relatively heavy material, which is adapted to be removably secured to the underside of a miniature toy vehicle body. The slug has on its bottom surface, a pair of downwardly opening recesses extending thereacross transversely to the direction of travel of the vehicle. A unitary bearing assembly is secured to the bottom surface of the slug and provides a relatively low friction mounting for a pair of axles having wheels rigidly mounted on the ends thereof. The bearing assembly includes a relatively flat elongated plastic insert member having downwardly opening bearing channels formed respectively at opposite ends thereof. The bearing channels are generally complementary, in their exterior configuration, to respective ones of the recesses in the slug and these channels are received in those recesses. The channels have opened end portions at opposite sides of the chassis and a wheel axle is loosely received in each of the channels with the ends thereof extending through the opening. A metal underplate of the same die cast material is provided adjacent the bottom surface of the insert and is substantially co-extensive therewith with portions of the insert covering the downwardly opened side of the channels to loosely retain the axles therebetween so as to permit free rotation of the axles under the momentum of the vehicle.

The slug has a pair of pins extending downwardly from the bottom surface thereof and the bearing insert and underplate have correspondingly aligned openings for receiving the pins. The latter may be frictionally engaged with the underplate to hold the assembly together or they may be staked, pinned, glued, or otherwise adhered to the underplate.

By this arrangement a unitary bearing assembly is provided in the chassis in the sense that the insert is a one-piece member having both bearing assemblies and is joined together with the underplate to define integral bearing channels. Since the insert is formed of a plastic material, preferably nylon, a low friction surface is provided surrounding the wheel axles so as to avoid any severe limitations on the speed or travel distance of the vehicle as a result of friction in the axle mounting. This is particularly important in extremely small-sized toy vehicles, such as sub-miniature racing cars, and those which are of approximately 1 inch in length or smaller since such small vehicles do not have much momentum as a result of their own weight. Accordingly, their speed and travel distance is limited and any frictional resistance to travel must be made as small as possible in order to increase the travel distance available in the vehicle. Further, the chassis is readily assembled since only three components are utilized, and these are merely snapped together and readily secured. Further, the chassis is adapted to be removably mounted in a vehicle body so that a single chassis can be used with a number of vehicle bodies.

The above, and other objects, features and advantages of this invention, will be apparent in the following detailed description of an illustrative embodiment thereof which is to be read in connection with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a chassis assembly constructed in accordance with the present invention and illustrating a racing car body, in dotted lines, to which the chassis may be secured;

FIG. 2 is a perspective view of the slug portion of the chassis assembly;

FIG. 3 is a perspective view illustrating primarily the bottom surface of the insert member of the chassis assembly inverted from the assembled position of FIG. 1;

FIG. 4 is a perspective view of the underplate of the chassis assembly;

FIG. 5 is a sectional view taken on line 55 of FIG. 1 illustrating a typical wheel mounting arrangement; and

FIG. 6 is a view similar to FIG. 5 illustrating another wheel mounting arrangement.

Referring to the drawings in detail, and initially to FIG. 1 thereof, it will be seen that a chassis assembly 10 embodying the present invention, as shown therein, is adapted to be removably mounted within the body of a toy vehicle 12 (shown in dotted lines). Chassis assembly 10 is formed of three main components, slug portion 14, an insert 16, and an underplate 18. These components are secured together to form an integral or unitary bearing assembly which provides a bearing channel for the axles of front and rear wheels 22, 24.

Slug 14, as seen in FIG. 2, is formed ofa die cast relatively heavy material such as Zamac and is a relatively flat structure having recesses 26 and 28 formed on its lower surface 30. These recesses are adapted to receive bearing blocks or channel bearings 32 formed respectively at the ends of the insert 16. The external configuration of each of the channels 32 is generally complementary to a respective one of the recesses 26 and 28 and these channels are received in the recesses, as illustrated in FIG. 1. The channels are interconnected by a flat strip or intermediate portion 33 which is of substantially the same width as the slug l4, and the entire insert 16, including the channels 32, is formed of a material which has a relatively low coefficient of friction, such as for example, molded nylon, acetal or Teflon.

Referring again to FIGS. 1 and 2 of the drawings, it is seen that the peripheral configuration of the slug 14 is generally rectangular and has projecting portions 34 and 36 at the front and rear thereof and projections 38 at the sides. These projections have inclined surfaces and provide shoulders 40 about the periphery of the vehicle. These shoulders may be utilized to snapfit the slug within body 12 so that the slug and the unitary bearing assembly is removably mounted within the body and can be selectively secured to any number of miniature vehicle bodies. Alternatively, the slug may be secured to the body in a number of other ways such as by screwing or gluing the slug to the body.

The bottom surface 30 of slug 14 is provided with at least one, and preferably two, depending pin members 42 which extend downwardly from surface 30. Insert 16 (whose lower surface is shown uppermost in FIG. 3 for convenience in illustrating channels 32) includes a pair of complementary apertures 44 which are adapted to loosely receive pins 42 so that the insert may be placed with its top surface 46 against surface 30 so that channels 32 can be inserted within recesses 26 and 28 respectively. The actual assembly is performed with the pins 42 uppermost.

With insert 16 adjacent surface 30 in this manner, the axles 20 of the vehicle may be placed in channels 32 and seated in the recesses or openings 48 in the sides 50 of the channels. These axles will, in the preferred embodiment of the present invention, already have the wheels 22, 24 (also formed of nylon) secured thereto and typically the axles 20 will be formed of a thin or small gauge wire and the wheels will be rigidly secured thereto. It is noted that the openings 48 in sides 50 of channel members 32 have a depth and width which is somewhat larger than the diameter of the wire axles so as to permit free rotation of the axles in the completed bearing. It will also be noted that the channel members 32 are longer than the width of the slug 14 or the insert 16 and extend therebeyond on both sides of the chassis. The recesses 48 are dimensioned to permit the axles also to move slightly in the vertical direction within the completed bearing assembly with the edges of the recesses acting as fulcrums for the axles. In this manner, irregularities in the play surface can be accommodated by movement between the vehicle body and the axles. This permits the miniature vehicles to go over slight bumps in the road or play surface so that the vehicle maintains a straight direction of travel with good tracking and no undesired changes in direction.

Referring to FIG. 5 of the drawings, it is seen that the wheels 22 have an axial bore 52 of substantially the same diameter as the wire axle 20 so that the wheel is frictionally engaged with the wire and secured thereto. The ends 54 of the wire are bent over, so as to prevent the wheels from coming off the axles. Similarly, in another embodiment, shown in FIG. 6, the ends of the axles may be treated so as to form heads 56 which provide the appearance of a hubcap or axle nut. The wheels 24 are secured to their axle 20 in the same manner selected for mounting front wheels 22. In either case the wheels 22, 24 are rigidly secured to their axles so as to rotate therewith. The wheels 22, 24 are provided with inwardly facing hub portions 25 that may engage the ends of the bearing channels 32 to limit the side-to-side movement of the wheel axle assemblies in a low friction manner. This construction also will unsure against frictional engagement of the wheels with the adjacent portion of the body 12.

After the axles and the wheels are assembled in this manner and placed in channels 32, the underplate 18 is secured to the pins 42. Underplate 18 is provided with a pair of apertures 60 which are adapted to receive pins 42 in close contact therewith so that the surface 62 of the underplate may be positioned against the bottom surface 64 of insert 16. In this manner, the end portions 66 and 68 of the underplate are positioned adjacent or against the opened ends 68 of channels 32 so as to define enclosed bearing members. The connection of pins 42 with underplate 18 forms an integral chassis member with the three components and having the wheeled axles mounted therein. The pins may be staked, glued or otherwise secured within the apertures 60 so as to form an integral assembly which is not readily separated by children during normal play. As a result, the entire chassis assembly is readily removable from one vehicle body and transferrable to another vehicle body.

In use the axles rotate in the upper portions of the channels 32. Because the channels 32 are formed of a material (preferably nylon), having relatively low coefficient of friction, the axles are subjected to extremely little drag due to the effects of friction and as a result the vehicle speed and the time the vehicle is able to coast under a given push force, and thus the distance of travel, are substantially increased. Similarly, the use of the heavy slug and plate adds weight to the vehicle to increase its momentum and thus also increase its travel distance.

Referring again to FIG. 1 of the drawings, it is seen that the illustrative embodiment of the invention illustrated is used in conjunction with a racing type subminiature toy vehicle. This vehicle is provided with rear wheels whose diameter is somewhat larger than the front wheels to simulate the actual design of full-scale automotive racing vehicles. Thus, the rear axle of the wheels 24 is at a somewhat higher location with respect to the base of the underplate 18 than is the axle for the front wheels 22. To achive this configuration, the recess 28 in slug 14 is made somewhat deeper than the recess 26, and the channel 32 corresponding to recess 28 is similarly made deeper. In addition, the rear portion 68 of insert 16 is formed as a raised surface, (FIG. 4) so as to close the opening of the rear channel 32 at a higher lever. As a result, a more pleasing toy is provided with no additional assembly work required. Additionally, the use of the larger rear wheels provides better tracking, road stability, and other similar advantages to the operation of the miniature vehicle.

In an alternate construction, not illustrated, the axle receiving channels may be formed entirely within the thickness of the plastic insert, thus obviating the necessity for providing the recesses in the slug. In yet another construction the recesses are made deeper than the channels so that independent movement of the channels vis-a-vis the slug is possible. This structure provides a more resilient axle support.

The slug 14 also includes a pair of depending front and rear extensions 70, which provided added mass to the slug. These extensions extend beyond surface 30 a distance equal to the combined total of the thicknesses of inserts l6 and underplate 18, so that a completely flat surface is provided to the underside of the vehicle when it is in its assembled configuration. This provides a more realistic appearance to the vehicle than has been attained with previously proposed constructions wherein the axles merely extend through holes in the vehicle body or in U-shaped clips extending from the vehicle body.

it will be readily understood by those skilled in the Art that the wheels 22 may have an axial bore 52 that is somewhat larger than the diameter of the wheel axle so that the wheel is freely rotatable on the axle. This is particularly advantageous when the structure of FIG. 6 is employed and the wheels are made of a material having a low coefficient of friction.

It is thus seen that a relatively simple and inexpensive chassis assembly is provided for miniature toy vehicles. The chassis assembly includes a unitary bearing construction which is readily assembled and which avoids the application of unnecessary friction to the wheel axles. The bearings are in a unitary construction so that standardized construction is accomplished with accurate spacing of the vehicle wheels in each toy manufactured. Moreover, the construction permits the removable mounting of the chassis and wheels to permit interchangeability of the vehicle body.

Although an illustrative embodiment of the present invention has been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to that precise embodiment and that various changes and modifications may be effected therein by one skilled in the Art without departing from the scope or spirit of this invention.

What is claimed is:

l. A chassis assembly for use in a miniature wheeled toy vehicle or the like wherein the toy vehicle is adapted to coast due to its own momentum, said chassis comprising a relatively flat slug adapted to be secured to a vehicle body, a relatively flat elongated insert member formed of a material having a low coefficient of friction and including a pair of bearing blocks formed respectively at opposite ends thereof, said bearing blocks defining a pair of downwardly opening channels, said channels having opened end portions at opposite sides of said chassis, a wheel axle loosely received in each of said channels with the ends thereof extending through said opening and having a pair of wheels respectively secured thereto, an underplate positioned on the bottom surface of said insert, substantially coextensive therewith, with portions of said underplate covering the downwardly open side of said channels to loosely retain said axles therein, and means for securing said slug, insert and underplate together to form a unitary toy vehicle chassis assembly.

2. The chassis assembly as defined in claim 1 wherein said slug has, on its bottom surface, a pair of downwardly opening recesses extending across the slug transversely to the direction of travel of the vehicle and wherein said bearing blocks are generally complementary to and are received in said recesses.

3. The chassis assembly of claim 2 wherein said bearing blocks are movable relative to said recesses.

4. The chassis assembly as defined in claim 1 wherein said underplate is formed of the same material as said slug.

5. The chassis assembly as defined in claim 1 wherein said material is nylon.

6. The chassis assembly as defined in claim 1 wherein said means for securing said slug, insert and underplate together includes a pair of pins extending downwardly from the bottom surface of said slug, said insert and said underplate each having a pair of spaced apertures therein for receiving said pins.

7. The chassis assembly as defined in claim 1 wherein the recess at the rear of said slug with respect to the direction of travel of said toy vehicle is deeper than the other recess whereby the rear axle in said chassis is located at a slightly higher elevation than the front axle.

8. The chassis assembly as defined in claim 1 wherein said wheels are formed of nylon and are rigidly secured to their associated axles.

9. The chassis assembly as defined in claim 8 wherein said channels have portions extending laterally of said slug.

10. The chassis assembly as defined in claim 9 wherein said wheels are each provided with inwardly directed hubs arranged to engage said channels with low friction.

11. A chassis assembly for use in a miniature wheeled toy vehicle or the like wherein the toy vehicle is adapted to coast due to its own momentum, said chassis comprising a relatively flat slug formed of die cast, relatively heavy material adapted to be secured to a vehicle body and having, on its bottom surface, a pair of downwardly opening recesses extending across the slug transversely to the direction of travel of the toy vehicle, and a unitary bearing assembly mounted on the bottom surface of said slug, said unitary bearing assembly including a relatively flat elongated insert member of bearing material having downwardly opening bearing channels formed respectively at opposite ends thereof, said channels being generally complementary in their exterior configuration, and received in respective ones of said recesses in said slug, said channels having opened end portions at opposite sides of said chassis, a wheel axle loosely received in each of said channels with the ends thereof extending through said openings, a wheel mounted adjacent each of said axle ends and an underplate on the bottom surface of said insert and substantially coextensive therewith, said insert having portions thereof covering the downwardly open side of said channels to loosely retain said axles therein and thereby permit free rotation of said axles under the momentum of the vehicle, said slug having at least one pin extending downwardly from the bottom surface thereof, for securing said unitary bearing assembly to said slug and said unitary bearing assembly having aligned openings in said insert and said underplate for receiving said pin.

12. The chassis as defined in claim 11 wherein said slug has two downwardly extending pins for securing said unitary bearing assembly thereto and said unitary bearing assembly has two pairs of aligned openings in said insert and underplate for receiving said pins.

13. The chassis assembly as defined in claim 11 wherein said bearing material is selected from the group of low coefficient of friction materials including nylon, acetal and Teflon.

14. The chassis assembly as defined in claim 13 wherein the recess at the rear'of said slug with respect to the direction of travel of said toy vehicle is deeper than the other recess whereby the rear axle in said chassis is located at a slightqhigher elevation than the front axle.

15. The chassis assembly as defined in claim 14 wherein said recesses are generally U-shaped and have relatively flat bight portions.

16. The chassis assembly as defined in claim 1 wherein said wheels are formed of a material having a low coefficient of friction and rotatably mounted on their associated axles.

17. The chassis assembly as defined in claim 11 wherein said wheels are formed of a material having a low coefficient of friction and are rigidly secured to their associated axles.

18. The chassis assembly 'as defined in claim 11 wherein said wheels are formed of a material having a low coefficient of friction and are rotatably mounted on their associated axles.

19. The chassis assembly as defined in claim 1 wherein said wheels are formed of a material having a low coefficient of friction and are rotatably mounted on their associated axles. 

1. A chassis assembly for use in a miniature wheeled toy vehicle or the like wherein the toy vehicle is adapted to coast due to its own momentum, said chassis comprising a relatively flat slug adapted to be secured to a vehicle body, a relatively flat elongated insert member formed of a material having a low coefficient of friction and including a pair of bearing blocks formed respectively at opposite ends thereof, said bearing blocks defining a pair of downwardly opening channels, said channels having opened end portions at opposite sides of said chassis, a wheel axle loosely received in each of said channels with the ends thereof extending through said opening and having a pair of wheels respectively secured thereto, an underplate positioned on the bottom surface of said insert, substantially coextensive therewith, with portions of said underplate covering the downwardly open side of said channels to loosely retain said Axles therein, and means for securing said slug, insert and underplate together to form a unitary toy vehicle chassis assembly.
 2. The chassis assembly as defined in claim 1 wherein said slug has, on its bottom surface, a pair of downwardly opening recesses extending across the slug transversely to the direction of travel of the vehicle and wherein said bearing blocks are generally complementary to and are received in said recesses.
 3. The chassis assembly of claim 2 wherein said bearing blocks are movable relative to said recesses.
 4. The chassis assembly as defined in claim 1 wherein said underplate is formed of the same material as said slug.
 5. The chassis assembly as defined in claim 1 wherein said material is nylon.
 6. The chassis assembly as defined in claim 1 wherein said means for securing said slug, insert and underplate together includes a pair of pins extending downwardly from the bottom surface of said slug, said insert and said underplate each having a pair of spaced apertures therein for receiving said pins.
 7. The chassis assembly as defined in claim 1 wherein the recess at the rear of said slug with respect to the direction of travel of said toy vehicle is deeper than the other recess whereby the rear axle in said chassis is located at a slightly higher elevation than the front axle.
 8. The chassis assembly as defined in claim 1 wherein said wheels are formed of nylon and are rigidly secured to their associated axles.
 9. The chassis assembly as defined in claim 8 wherein said channels have portions extending laterally of said slug.
 10. The chassis assembly as defined in claim 9 wherein said wheels are each provided with inwardly directed hubs arranged to engage said channels with low friction.
 11. A chassis assembly for use in a miniature wheeled toy vehicle or the like wherein the toy vehicle is adapted to coast due to its own momentum, said chassis comprising a relatively flat slug formed of die cast, relatively heavy material adapted to be secured to a vehicle body and having, on its bottom surface, a pair of downwardly opening recesses extending across the slug transversely to the direction of travel of the toy vehicle, and a unitary bearing assembly mounted on the bottom surface of said slug, said unitary bearing assembly including a relatively flat elongated insert member of bearing material having downwardly opening bearing channels formed respectively at opposite ends thereof, said channels being generally complementary in their exterior configuration, and received in respective ones of said recesses in said slug, said channels having opened end portions at opposite sides of said chassis, a wheel axle loosely received in each of said channels with the ends thereof extending through said openings, a wheel mounted adjacent each of said axle ends and an underplate on the bottom surface of said insert and substantially coextensive therewith, said insert having portions thereof covering the downwardly open side of said channels to loosely retain said axles therein and thereby permit free rotation of said axles under the momentum of the vehicle, said slug having at least one pin extending downwardly from the bottom surface thereof, for securing said unitary bearing assembly to said slug and said unitary bearing assembly having aligned openings in said insert and said underplate for receiving said pin.
 12. The chassis as defined in claim 11 wherein said slug has two downwardly extending pins for securing said unitary bearing assembly thereto and said unitary bearing assembly has two pairs of aligned openings in said insert and underplate for receiving said pins.
 13. The chassis assembly as defined in claim 11 wherein said bearing material is selected from the group of low coefficient of friction materials including nylon, acetal and Teflon.
 14. The chassis assembly as defined in claim 13 wherein the recess at the rear of said slug with respect to the direction of travel of said toy vehicle is deeper than the other reCess whereby the rear axle in said chassis is located at a slight higher elevation than the front axle.
 15. The chassis assembly as defined in claim 14 wherein said recesses are generally U-shaped and have relatively flat bight portions.
 16. The chassis assembly as defined in claim 1 wherein said wheels are formed of a material having a low coefficient of friction and rotatably mounted on their associated axles.
 17. The chassis assembly as defined in claim 11 wherein said wheels are formed of a material having a low coefficient of friction and are rigidly secured to their associated axles.
 18. The chassis assembly as defined in claim 11 wherein said wheels are formed of a material having a low coefficient of friction and are rotatably mounted on their associated axles.
 19. The chassis assembly as defined in claim 1 wherein said wheels are formed of a material having a low coefficient of friction and are rotatably mounted on their associated axles. 